fractionation in the system methane-hydrogen-water

Horibe, Yoshio; Craig, H.

doi:10.1016/0016-7037(95)00391-6

Cited by 164 publications

(190 citation statements)

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“…Microbial H 2 consumption has been shown to catalyze nonproductive H 2 -water exchange and drive the δ 2 H of H 2 toward isotopic equilibrium with water on a monthly time scale (24). The expected δ 2 H value for H 2 in equilibrium with Lake Vida water at −13.4°C is −850‰ (25), which indicates isotopic disequilibrium. Isotopic equilibrium between H 2 and water is expected, however, to take between 1,000 and 10,000 y (22), perhaps longer at the temperature of Lake Vida.…”

Section: Resultsmentioning

confidence: 94%

Microbial life at −13 °C in the brine of an ice-sealed Antarctic lake

Murray

Kenig

Fritsen

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

160

190

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The permanent ice cover of Lake Vida (Antarctica) encapsulates an extreme cryogenic brine ecosystem (−13°C; salinity, 200). This aphotic ecosystem is anoxic and consists of a slightly acidic (pH 6.2) sodium chloride-dominated brine. Expeditions in 2005 and 2010 were conducted to investigate the biogeochemistry of Lake Vida's brine system. A phylogenetically diverse and metabolically active Bacteria dominated microbial assemblage was observed in the brine. These bacteria live under very high levels of reduced metals, ammonia, molecular hydrogen (H 2 ), and dissolved organic carbon, as well as high concentrations of oxidized species of nitrogen (i.e., supersaturated nitrous oxide and ∼1 mmol·L −1 nitrate) and sulfur (as sulfate). The existence of this system, with active biota, and a suite of reduced as well as oxidized compounds, is unusual given the millennial scale of its isolation from external sources of energy. The geochemistry of the brine suggests that abiotic brine-rock reactions may occur in this system and that the rich sources of dissolved electron acceptors prevent sulfate reduction and methanogenesis from being energetically favorable. The discovery of this ecosystem and the in situ biotic and abiotic processes occurring at low temperature provides a tractable system to study habitability of isolated terrestrial cryoenvironments (e.g., permafrost cryopegs and subglacial ecosystems), and is a potential analog for habitats on other icy worlds where water-rock reactions may cooccur with saline deposits and subsurface oceans.astrobiology | geomicrobiology | microbial ecology | extreme environment T he observation of microbes surviving and growing in a variety of icy systems on Earth has expanded our understanding of how life pervades, functions, and persists under challenging conditions (e.g., refs. 1-3). Studies of the physical characteristics, the geochemical properties, and microbes in ice (triple point junctions, brine channels, gas bubbles) have also changed our perceptions of the environments that may contain traces of, or even sustain, life beyond Earth [e.g., Mars (4), Europa (5), and Enceladus (6)].Solute depression of ice crystal formation or solar radiation melting of water ice are key processes that provide liquid waterthe key solvent that makes life possible-within icy systems. Microbial communities in these conditions are often sustained by a supply of energy that ultimately derives from photosynthesis (present or past). The understanding of ecosystems based on energy sources other than the Sun comes mainly from realms where hydrothermal processes have provided reduced compounds necessary to fuel chemosynthetically driven ecosystems. Methane derived from thermogenic or biogenic sources can also support microbial communities in deep sea (7) and high arctic cold saline seeps (8). More recently, discoveries of life and associated processes in deep terrestrial subsurface ecosystems (9) provide compelling evidence of subsurface life that in some cases is fueled by nonphotosynthetic processes. Ou...

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Section: Resultsmentioning

confidence: 94%

Microbial life at −13 °C in the brine of an ice-sealed Antarctic lake

Murray

Kenig

Fritsen

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

160

190

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“…However, it is highly unlikely such a mechanism could be used to achieve the same result under hydrothermal conditions given the demonstrated potential for aqueous ketone oxidation at elevated temperatures ). An approach similar to HORIBE and CRAIG (1995), whereby gaseous mixtures of CH 4 and H 2 were isotopically equilibrated over a Ni-Thoria catalyst, might be possible for low molecular weight alkanes and water, but this is speculative and would not allow for carbon-specific H equilibration.…”

Section: Discussionmentioning

confidence: 99%

“…Based on the experimental observations of reversible exchange presented here, this discrepancy may actually reflect partial or complete alkane-water H isotope exchange in the latter cases. The recent advent of theoretical equilibrium fractionation factors for C 2+ alkane H below 100°C mentioned above (WANG et al, 2009a,b), combined with α o/w values for CH 4 -H 2 O equilibrium (HORIBE and CRAIG, 1995) at the reported temperatures in these studies.…”

Section: H / 1 H Ratios and Abiogenesis In Igneous Environmentsmentioning

confidence: 96%

Laboratory and field-based investigations of subsurface geochemical processes in seafloor hydrothermal systems

Reeves¹

2010

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This thesis presents the results of four discrete investigations into processes governing the organic and inorganic chemical composition of seafloor hydrothermal fluids in a variety of geologic settings. Though Chapters 2 through 5 of this thesis are disparate in focus, each represents a novel investigation aimed at furthering our understanding of subsurface geochemical processes affecting hydrothermal fluid compositions. Chapters 2 and 3 concern the abiotic (nonbiological) formation of organic compounds in high temperature vent fluids, a process which has direct implications for the emergence of life in early Earth settings and sustainment of present day microbial populations in hydrothermal environments. Chapter 2 represents an experimental investigation of methane (CH 4 ) formation under hydrothermal conditions. The overall reduction of carbon dioxide (CO 2 ) to CH 4 , previously assumed to be kinetically inhibited in the absence of mineral catalysts, is shown to proceed on timescales pertinent to crustal residence times of hydrothermal fluids. In Chapter 3, the abundance of methanethiol (CH 3 SH), considered to be a crucial precursor for the emergence of primitive chemoautotrophic life, is characterized in vent fluids from ultramafic-, basalt-and sediment-hosted hydrothermal systems. Previous assumptions that CH 3 SH forms by reduction of CO 2 are not supported by the observed distribution in natural systems. Chapter 4 investigates factors regulating the hydrogen isotope composition of hydrocarbons under hydrothermal conditions. Isotopic exchange between low molecular weight n-alkanes and water is shown to be facilitated by metastable equilibrium reactions between alkanes and their corresponding alkenes, which are feasible in natural systems. In Chapter 5, the controls on vent fluid composition in a backarc hydrothermal system are investigated. A comprehensive survey of the inorganic geochemistry of fluids from sites of hydrothermal activity in the eastern Manus Basin indicates that fluids there are influenced by input of acidic magmatic solutions at depth, and subsequently modified by variable extents of seawater entrainment and mixing-related secondary acidity production. CHAPTER 1 IntroductionSeafloor hydrothermal systems associated with the generation of oceanic crust represent a dramatic expression of heat and mass transfer from the interior of the Earth. In addition to profound effects on ocean chemistry, convective circulation of seawater through volcanically active oceanic crust leads to the formation of metal sulfide deposits. In addition, seafloor hot springs are often invoked as ideal settings from which early microbial life could have emerged.Since the initial discovery of low temperature venting at the Galápagos Spreading Center in 1977 (CORLISS et al., 1979), our understanding of the composition and diversity of hydrothermal solutions has expanded greatly. During convection through oceanic crust of basaltic composition, O 2 -replete seawater reacts with crustal rock, typically producin...

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“…One mechanism than can cause 2 H depletion in CH 4 is isotopic exchange of hydrogen with formation water. Fractionation factors calculated for temperatures of 200-300°C that are based on exchange experiments between water and methane (Horibe and Craig, 1995) (Breen et al, 1985;Dresel, 1985). Methane equilibrated with water of this composition at temperatures of maximum burial in the Appalachian basin will have d 2 H compositions of about À183‰ to À160‰, well within the range needed for a possible end member.…”

Section: Late Stage Methane Reactionsmentioning

confidence: 99%

Carbon and hydrogen isotopic reversals in deep basin gas: Evidence for limits to the stability of hydrocarbons

Burruss

Laughrey

2010

Organic Geochemistry

268

139

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a b s t r a c tDuring studies of unconventional natural gas reservoirs of Silurian and Ordovician age in the northern Appalachian basin we observed complete reversal of the normal trend of carbon isotopic composition, such that d 13 C methane (C 1 ) >d 13C ethane (C 2 ) >d 13 C propane (C 3 ). In addition, we have observed isotopic reversals in the d 2 H in the deepest samples. Isotopic reversals cannot be explained by current models of hydrocarbon gas generation. Previous observations of partial isotopic reversals have been explained by mixing between gases from different sources and thermal maturities. We have constructed a model which, in addition to mixing, requires Rayleigh fractionation of C 2 and C 3 to cause enrichment in 13 C and create reversals. In the deepest samples, the normal trend of increasing enrichment of 13 C and 2 H in methane with increasing depth reverses and 2 H becomes depleted as 13 C becomes enriched. We propose that the reactions that drive Rayleigh fractionation of C 2 and C 3 involve redox reactions with transition metals and water at late stages of catagenesis at temperatures on the order of 250-300°C. Published ab initio calculated fractionation factors for C-C bond breaking in ethane at these temperatures are consistent with our observations. The reversed trend in d 2 H in methane appears to be caused by isotopic exchange with formation water at the same temperatures. Our interpretation that Rayleigh fractionation during redox reactions is causing isotopic reversals has important implications for natural gas resources in deeply buried sedimentary basins.Published by Elsevier Ltd.

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fractionation in the system methane-hydrogen-water

Cited by 164 publications

References 13 publications

Microbial life at −13 °C in the brine of an ice-sealed Antarctic lake

Microbial life at −13 °C in the brine of an ice-sealed Antarctic lake

Laboratory and field-based investigations of subsurface geochemical processes in seafloor hydrothermal systems

Carbon and hydrogen isotopic reversals in deep basin gas: Evidence for limits to the stability of hydrocarbons

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